Photoreception in Euglena gracilis [Mastigophora]: Fluence-rate and time dependence of photoaccumulation and photodispersal

• Published in: Journal of Plant Research Vol. 111; no. 1103; pp. 431 - 440
• Main Authors: GeiB, D. (Philipps-Univ., Marburg (Germany)), Senger, H, Galland, P
• Format: Journal Article
• Language: English; Japanese
• Published: The Botanical Society of Japan 01.09.1998
• Subjects: blue light; duration; Euglena gracilis; FOTORECEPTORES; FOTOSENSIBILIDAD; interception; light; light intensity; lighting; MASTIGOPHORA; mutants; OPTICAL PROPERTIES; PHOTORECEPTEUR; PHOTORECEPTORS; PHOTOSENSIBILITE; PHOTOSENSITIVITY; photosynthesis; phototaxis; PROPIEDADES OPTICAS; PROPRIETE OPTIQUE; red light; wavelengths
• ISSN: 0918-9440; 1618-0860
• DOI: 10.1007/bf02507808

The fluence-rate and time dependence for photoaccumulation and photodispersal of Euglena gracilis was measured for the wild-type strain and three white mutants. For wavelengths of 453 or 463 nm the threshold for photoaccumulation was close to 6 x 10(-2) Wm(-2). Photoaccumulation increased steadily with time and reached a maximum after about 4 hr. Red light elicited substantial photoaccumulation in the wild type and photodispersal in the white, non-photosynthetic mutant 1224-5/9f. The chromophore mediating the red-light response needs to be a non-photosynthetic pigment which remains presently unidentified. A white Euglena mutant, FB, which had retained a reduced stigma and a paraflagellar body, showed weak photoaccumulation. Two white mutants, 1224-5/1f and 1224-5/9f, both of which lacked the stigma and positive phototaxis, displayed during the first 90 min of irradiation photodispersal; after longer irradiations they showed instead photoaccumulation. These results contradict a widely held belief that the presence of a stigma represents a stringent requirement for photoaccumulation. Our results imply that phototaxis is not a prerequisite for photoaccumulation. Exogenous flavins and 5, 10-methenyl-tetrahydrofolate (MTHF) influenced in a wavelength-dependent manner photoaccumulation and photodispersal. In the wild type FAD and riboflavin (RB) caused at 453 nm an increase of the responsiveness for photoaccumulation. The photoaccumulation of the white mutant FB, was sensitized by FMN and FAD. In the white mutant 1224-5/9f exogenous flavins lowered the threshold for photodispersal. FMN, which absorbs only blue light, altered also the responsiveness to red light: in the wild type FMN reduced photoaccumulation and in the white mutant 1224-5/9f it reduced photodispersal